Archive.org has The Amateur Scientist by C.L. Stong available for free on their site! The work went out of print in 1972 and is considered a much sought after resource for amateur scientists and collectors. It features 57 projects from Stong and is available to read online or download here. From wikipedia:
The Amateur Scientist was a column in the Scientific American, and was the definitive “how-to” resource for citizen-scientists for over 72 years (1928–2001), making it the longest running column in Scientific American’s history. The column was regarded for revealing the brass-tacks secrets of research and showing home-based experimenters how to make original discoveries using only inexpensive materials. Since its début in 1928, “The Amateur Scientist” was a primary resource for science fair projects. It also inspired amateur experimenters, launched careers in science, and enjoyed a place of honor in classrooms and school libraries all over the world.
Although always accessible to an amateur’s budget, projects from “The Amateur Scientist” were often elegant and sophisticated. Some designs were so innovative that they set new standards in a field. Indeed, professionals continue to borrow from “The Amateur Scientist” to find low-cost solutions to real-world research problems.